Circumferential grooves and other features such as shoulders and beads may be formed in pipe elements by various methods, one of particular interest being roll grooving. Roll grooving methods involve engaging an inner roller with an inner surface of a pipe element and an outer roller with an outer surface of the pipe element opposite to the inner roller and incrementally compressing the sidewall of the pipe element between the rollers while rotating at least one of the rollers. Rotation of one roller (often the inner roller) causes relative rotation between the roller set and the pipe element, and features on the inner and outer rollers form corresponding features on the inner and outer surfaces of the pipe element. In one example roll grooving method the rollers remain in a fixed location and the pipe element rotates about its longitudinal axis relative to the rollers. In another example embodiment the pipe element remains stationary and the roller set traverses the pipe element's circumference.
One disadvantage of roll grooving is manifest when forming a circumferential groove in the outer surface of the pipe element near an open end. The circumferential groove is formed when a raised circumferential feature on the outer roller cooperates with a circumferential recess on the inner roller positioned opposite to the raised feature. During groove formation, the open end of the pipe element may become enlarged at the end of the pipe element; the end takes on a “bell” shape, flaring outwardly as an unwanted consequence when the material of the pipe is deformed to form the groove. Pipe end flare is unwanted because it can change the critical outer diameter of the pipe element at the end where it is most important not to exceed a maximum tolerance so that, for example, the pipe element may properly engage mechanical fittings or couplings and form a fluid tight joint. There is clearly a need for grooving rollers and a method of roll grooving which mitigates or eliminates pipe end flare.
Furthermore, pipe elements joined by mechanical couplings often use a flexible seal or gasket to effect a fluid tight seal. The gasket has sealing surfaces that are compressed against the outer surfaces of the pipe elements by the couplings. It is advantageous to improve the surface finish of the pipe elements in the region where they are engaged by the sealing surfaces to provide effective surface contact to ensure a good seal.